DT-PS No. 10 28 524 discloses a method of coating or impregnating textiles with a coating of polyalkylene oxide and the use of said coating as an antistatic, soil-repellent and water absorbing coating. A similar method is disclosed in DT-AS No. 22 39 592, which is specifically directed to a method of improving the stability of the coating by adding a cationic antistatic agent in the form of a reactive alkyl ethylene-urea and by performing the curing operation at elevated temperatures in the presence of moisture as a catalyst. According to both these references the preferred method for obtaining a cured coating seems to be the use of a polyalkylene oxide having at least two unsaturated groups in the form of acrylic, methacrylic and/or vinyl groups at the ends of the molecule or in side chains which groups are crosslinked by means of thermally activated initiators at elevated temperatures. Furthermore, these previously known methods require several process steps. It is true that DT-AS No. 22 39 592 mentions as an alternative the use of a mixture of a polyalkylene glycol with a polymerizable vinyl group in one end thereof and a vinyl monomer with at least two vinyl groups, but said alternative is in no way disclosed as any preferred alternative. Furthermore, said German citation neither discloses nor suggests the essential combination of features necessary according to the present invention or even less the outstanding combination of properties obtained by the present invention. Finally, no stabilization treatment is required in connection with the present invention as is required according to DT-AS No. 22 39 592.
Thus, as will be described more in detail below the present invention relates merely to polyethylene oxide as a coating material, which means essential advantages as compared to the use of other polyalkylene oxides, primarily thanks to the structural compatibility between the ethylene oxide units and the water molecules. However, the major difference relative to the prior art is not the use of polyethylene oxide per se but rather the following combination of features: the presence of ethylenically unsaturated groups at one end of the polyethylene oxide chains only, the way of accomplishing the cross-linking of the polyethylene oxide chains to obtain a stable coating on the substrate to be coated, viz. by radiation curing, and the swelling of the substrate prior to cross-linking. These major differences relative to the prior art impart to the manufactured article a unique structure of densely packed non-modified polyethylene oxide chains pendant from the substrate as well as a firm anchoring of the coating to the substrate.
As to the radiation curing this is a curing technique known per se, as is disclosed e.g. in EP, No. A1, 0 057 906. However, as was mentioned above the present invention is based on a combination of features, of which radiation curing is one only, giving results which are not in any way disclosed or suggested in the prior art.
SE Patent Application Ser.No. 8202524-8 discloses a method of applying to a polymeric substrate a hydrophilic coating of polyethylene oxide and its use in medical articles to be inserted into the human body. The polyethylene oxide is applied to the surface by swelling and curing at elevated temperature and in the presence of steam. Said known method differs from the present invention in that there are no unsaturated groups in the polyethylene oxide and that the cross-linking reactions are accomplished by means of a compound containing at least two non-reacted isocyanate groups and in the presence of a catalyst. A major drawback with this known method and with other prior art not utilizing the polyethylene oxide chain structure used according to the preesnt invention is, however, that during the cross-linking reaction the polyethylene oxide chains form loops at several reaction sites which means a poor degree of coating and an article that is less useful for practical purposes. This drawback is definitely eliminated by the present invention in that the structures of the reactions do not enable the formation of such loops. Furthermore, the process according to the present invention is much simpler than the method disclosed in the Swedish citation, as said method comprises several lengthy steps.
In connection with the prior art it should also be noted that the water-binding ability of polyethylene oxide is known per se and that said ability is utilized e.g. when impregnating wood to prevent dessication and the formation of cracks. Polyethylene oxide is also utilized when impregnating synthetic materials to impart antistatic properties thereto and in nonionic dispersants which adsorb and hydrophilize the surfaces of those particles and drops to be dispersed.